This invention relates to systems and processes designed to treat monoethylene glycol (MEG) used in the oil and gas industry, especially in offshore locations, to control the formation of hydrates. More particularly, the invention relates to MEG reclamation or regeneration processes that are designed to remove divalent cations from a rich MEG feed stream.
In the oil and gas industry, lean (dry) MEG is mixed with the water in a produced stream to control the formation of hydrates within the stream. The now rich (wet) MEG is, in turn, dried by way of a MEG reclamation or MEG regeneration process so that the MEG can be re-used in hydrate control. The lean MEG cannot be recovered by simply distilling the rich MEG and water in conditions of high salt concentration because the rich MEG is loaded with dissolved salt ions from the produced water. Sodium chloride is commonly the most concentrated salt in the produced water, but it may also contain dissolved divalent salts of magnesium, calcium, strontium, and barium. If these divalent cations are not removed or controlled at a low concentration, their high solubility in MEG will alter the physical properties of the MEG, eventually leading to failure of the reclamation or regeneration process.
In the current process for separating divalent cations from the rich MEG feed stream, the ions react with carbonate or hydroxide anions to form insoluble salt crystals, which are then removed from the feed stream. This process generally requires the addition of caustic and acid to completely remove the divalent cations and to neutralize the feed stream before it enters the MEG reclamation or MEG regeneration process.
The time and temperature of the current separation process must be strictly controlled. In addition, the process requires large and expensive equipment, as well as additional chemicals that are not inherently available as part of the MEG reclamation or MEG regeneration process. These chemicals must be obtained from outside sources which can be very expensive, particularly when delivered to offshore platforms in remote parts of the world. The chemicals may also be a safety concern, require specialized handling and storage, and increase training, reporting, and recordkeeping requirements. The current separation process also produces a carbonate salt in the form of a solid or slurry material that is generally insoluble and requires disposal as a waste. Proper disposal of this material can be expensive, time-consuming, and labor-intensive. Disposal is even more difficult in offshore applications where temporary storage space and transportation to an approved disposal site are not readily available.
A need exists for systems and processes for removing divalent cations from rich MEG feed streams in order to improve the efficiency of the MEG reclamation or MEG regeneration process and to prevent the accumulation of salts inside the process equipment. A need also exists for systems and processes that are less expensive, easier to operate, do not require large amounts of space or additional chemicals, and facilitate the disposal of process waste streams.